Rosetta carried out its final manoeuvre, setting it on a collision course with the comet from an altitude of about 19 km. Rosetta had targeted a region on the small lobe of Comet, close to a region of active pits in the Ma’at region.
Pits are of particular interest because they play an important role in the comet’s activity. They also provide a unique window into its internal building blocks.
The descent gave Rosetta the opportunity to study the comet’s gas, dust and plasma environment very close to its surface, as well as take very high-resolution images.
The information collected on the descent to this fascinating region was returned to Earth before the impact.
The final image was taken from an altitude of 66 feet (20 meters) above the comet’s surface by the spacecraft’s OSIRIS wide-angle camera on Sept. 30. The initial report of 167 feet, or 51 meters, was based on the predicted impact time.
Now that the time has been confirmed, and following additional information and timeline reconstruction, the estimated distance has been updated. Analysis is ongoing.
The decision to end the mission on the surface is a result of Rosetta and the comet heading out beyond the orbit of Jupiter again. Further from the Sun than Rosetta has ever journeyed before, there would be little power to operate the craft.
Mission operators were also faced with an imminent month-long period when the Sun is close to the line-of-sight between Earth and Rosetta, meaning communications with the craft would have become increasingly more difficult.
Many surprising discoveries have already been made during the mission.
Scientists now believe that the comet’s two lobes formed independently, joining in a low-speed collision in the early days of the Solar System.
Long-term monitoring has also shown just how important the comet’s shape is in influencing its seasons, in moving dust across its surface, and in explaining the variations measured in the density and composition of the coma, the comet’s atmosphere.
Some of the most unexpected and important results are linked to the gases streaming from the comet’s nucleus, including the discovery of molecular oxygen and nitrogen, and water with a different ‘flavour’ to that in Earth’s oceans.
Rosetta did not disappoint, detecting the amino acid glycine, which is commonly found in proteins, and phosphorus, a key component of DNA and cell membranes. Numerous organic compounds were also detected.
Comets are time capsules containing primitive material left over from the epoch when the Sun and its planets formed.
While the operational side of the mission has finished today, the science analysis will continue for many years to come.
